Charl Els, a U of A psychiatrist and addictions specialist, argues it isn’t. It might seem obvious that it’s a bad idea to light up before starting a shift in jobs such as transportation, construction, health care and law enforcement. But according to Els’ research, impairment from cannabis can last far longer than once thought—in some cases more than 24 hours, even weeks for chronic users suffering withdrawal.

In a paper published late last year in the Canadian Journal of Addiction, Els’ conclusion is unequivocal: “Single or recurrent marijuana consumption is not recommended for persons who perform safety sensitive tasks” because it “has been demonstrated to have an adverse impact on a range of cognitive functions, as well as be associated with performance deficits.”

The challenge of measuring pot impairment

In analyzing metadata on vehicular collisions, for example, he concluded that the risk of crashing after marijuana consumption is roughly double—a good starting point for assessing risk in comparable activities demanding attention and sound decision-making.

“For the most part, we think four to six hours after consumption is roughly sufficient for the impairment to wash out,” said Els. “The problem is, the certainty of that is low. There is sufficient evidence to say it can last longer than 24 hours. If people consume in the evening, they can still be impaired in the morning, and Health Canada endorses that position."

Canadian law does not currently allow for mandatory drug testing by employers, as does American law, so it falls on employees to decide whether they are fit for work, said Els.

“An individual might feel he or she is just fine, has always used it and doesn't feel impaired” when they may not be functioning at full capacity.

And because people respond differently to THC, with varying levels of tolerance, and because the cannabinoid can remain stored in the body’s fat cells long after consumption, testing is unreliable anyway.

“Workplace drug testing does not measure impairment, but only the presence of the parent compound (THC) or its metabolites. Unlike alcohol, we don't have a legal standard for what constitutes impairment,” said Els. “We don't yet have a blood test or anything that's accepted on a regulatory level to determine impairment.”

Once marijuana is legalized, employers will no longer be able to enforce a drug-free workplace, because the law allowing them to do so only exists in the Criminal Code, “so if you remove that piece, we need a replacement of that regulation," he said.

Regulatory void needs to be filled

According to Els, the potentially dangerous quagmire of pot in the workplace hasn’t received the attention it deserves. He points to a discussion document released last year by Health Canada containing a total of just 32 words on the subject.

A federal task force on cannabis legalization and regulation, led by Anne McLellan, has since devoted about a page to workplace safety in its final report. It recognizes the challenges of cannabis on the job, among them “reasonable accommodation of employees who use cannabis for medical purposes or who may be dealing with dependence or other problematic use.” But the report does not make any specific recommendations beyond suggesting limits to cannabis-impaired driving.

“We know it's now on the table but there's a bunch of significant gaps in various areas,” said Els.

Waking up to withdrawal

Contrary to popular belief, cannabis dependence is now recognized as a genuine addiction in the medical community, said Els, both psychologically and physiologically, complete with symptoms of withdrawal. They occur when the brain adapts to large amounts of the drug by reducing production of and sensitivity to its own endocannabinoid neurotransmitters.

That means even if a chronic user quits just before starting a safety-sensitive job, withdrawal symptoms can persist for up to three weeks.

"Withdrawal was previously downplayed, but we now have sufficient evidence to say there is impairment associated with withdrawal,” said Els. “The biggest problem is the sleep disruption. Almost half of individuals coming off marijuana do display measurable sleep deprivation, and fatigue can also be a bona fide impairment factor."

Despite marijuana’s reputation as a sleep aid, he added, in the long run it is anything but.

"It gives the erroneous impression that it helps with sleep, but when you look at the actual quality of it, that's a different story."

Els stresses he is not against legalization of marijuana, nor does he argue his recommendations should necessarily apply to workplaces where safety is not a primary concern.

But there is no question, he said, Canada must come up quickly with a standard to measure impairment related to cannabis, one enshrined in the law, similar to the breathalyzer for alcohol. And with legalization on track by July 2018, there isn’t much time to get it done.

"In an ideal world we want to ensure that safety is paramount, but we also want to protect freedom of self-determination,” said Els. “The best we can do is perhaps delay the legalization of marijuana until we've met a certain set of criteria that allows us to proceed with safety."